231 research outputs found
Bose-Einstein condensation of chromium
We report on the generation of a Bose-Einstein condensate in a gas of
chromium atoms, which will make studies of the effects of anisotropic
long-range interactions in degenerate quantum gases possible. The preparation
of the chromium condensate requires novel cooling strategies that are adapted
to its special electronic and magnetic properties. The final step to reach
quantum degeneracy is forced evaporative cooling of 52Cr atoms within a crossed
optical dipole trap. At a critical temperature of T~700nK, we observe
Bose-Einstein condensation by the appearance of a two-component velocity
distribution. Released from an anisotropic trap, the condensate expands with an
inversion of the aspect ratio. We observe critical behavior of the condensate
fraction as a function of temperature and more than 50,000 condensed 52Cr
atoms.Comment: 4 pages, 4 figure
Observation of Feshbach resonances in an ultracold gas of Cr
We have observed Feshbach resonances in elastic collisions between ultracold
Cr atoms. This is the first observation of collisional Feshbach
resonances in an atomic species with more than one valence electron. The zero
nuclear spin of Cr and thus the absence of a Fermi-contact interaction
leads to regularly-spaced resonance sequences. By comparing resonance positions
with multi-channel scattering calculations we determine the s-wave scattering
length of the lowest potentials to be
\unit[112(14)]{a_0}, \unit[58(6)]{a_0} and -\unit[7(20)]{a_0} for S=6, 4,
and 2, respectively, where a_{0}=\unit[0.0529]{nm}.Comment: 4 pages, 2 figures, 1 tabl
Determination of the s-wave Scattering Length of Chromium
We have measured the deca-triplet s-wave scattering length of the bosonic
chromium isotopes Cr and Cr. From the time constants for
cross-dimensional thermalization in atomic samples we have determined the
magnitudes and ,
where . By measuring the rethermalization rate of Cr over a
wide temperature range and comparing the temperature dependence with the
effective-range theory and single-channel calculations, we have obtained strong
evidence that the sign of is positive. Rescaling our Cr
model potential to Cr strongly suggests that is positive,
too.Comment: v3: corrected typo in y-axis scaling of Figs. 3 and
Continuous loading of a magnetic trap
We have realized a scheme for continuous loading of a magnetic trap (MT).
^{52}Cr atoms are continuously captured and cooled in a magneto-optical trap
(MOT). Optical pumping to a metastable state decouples atoms from the cooling
light. Due to their high magnetic moment (6 Bohr magnetons), low-field seeking
metastable atoms are trapped in the magnetic quadrupole field provided by the
MOT. Limited by inelastic collisions between atoms in the MOT and in the MT, we
load 10^8 metastable atoms at a rate of 10^8 atoms/s below 100 microkelvin into
the MT. After loading we can perform optical repumping to realize a MT of
ground state chromium atoms.Comment: 4 pages, 4 figures, version 2, modified references, included
additional detailed information, minor changes in figure 3 and in tex
Optimized loading of an optical dipole trap for the production of Chromium BECs
We report on a strategy to maximize the number of chromium atoms transferred
from a magneto-optical trap into an optical trap through accumulation in
metastable states via strong optical pumping. We analyse how the number of
atoms in a chromium Bose Einstein condensate can be raised by a proper handling
of the metastable state populations. Four laser diodes have been implemented to
address the four levels that are populated during the MOT phase. The individual
importance of each state is specified. To stabilize two of our laser diode, we
have developed a simple ultrastable passive reference cavity whose long term
stability is better than 1 MHz
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